NU1505: Duplicate 'PackageDownload' items warning is raised when the SDK uses PackageDownload to get packages.

[nkolev92]

Describe the bug

Recently NuGet added warnings for duplicate PackageReference/PackageDownload/PackageVersion items. Duplicate items could lead to an unpredictable behavior. You can learn about the motivation more in NuGet/Home#9864.
https://github.com/NuGet/Home/blob/dev/proposed/2022/duplicate-nuget-item-error-handling.md

NuGet added this in 6.0.400, so customers will start seeing this very soon.

To Reproduce

Originally filled in NuGet/Home#11720.

1. Use latest SDK with NuGet version 6.3.0 or higher. Might not be 100% inserted today.
2. Create a .NET Core Console App, netcoreapp3.1. project with PackageReference package installed.
3. Run “dotnet restore” in Developer Command Prompt for VS 2022 Preview
4. The warning “warning NU1505: Duplicate 'PackageDownload' items found. Remove the duplicate items or use the Update functionality to ensure a consistent restore behavior.” occurs as below screenshot.

This was was discovered by the NuGet test team, @v-luzh Can you please post the csproj in question?

Why is this important?

NuGet will raise a warning when it sees duplicate items, and warning as errors could cause failures for customers.

Exceptions (if any)

Further technical details

• Include the output of dotnet --info
• The IDE (VS / VS Code/ VS4Mac) you're running on, and its version
  Latest main version of NuGet tooling will have this.

[v-crchang]

@nkolev92 The repro project: Netcoreapp.zip

[Shyam-Gupta]

I am also hitting this issue while building WinForms designer repo locally: https://github.com/dotnet/winforms-designer.
It is a private repo.

[baronfel]

We appear to be adding multiple copies of the same apphost during the ResolveAppHosts task: